<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script type="text/javascript">
        //一次性声明多个变量
        var a = 10,
            b = 20,
            c = 30,
            d = 40,
            e;
        //原始值
        //Number String Boolean undefined null

        //引用值
        //array object function ..... date reg
    </script>
</body>

</html>